This invention relates in general to a process for manufacturing bullets and, more particularly, to a method for manufacturing bullets having improved accuracy and increased weight.
There are a wide variety of projectiles or bullets for use with firearms, with the various bullets having specific characteristics designed according to the purpose, or type of target, at which the bullet is to be fired. The outer shape of the bullet is designed in order to achieve a favorable ballistic trajectory. Conventional bullets are tapered from a point at the nose of the bullet to the cylindrical portion of the bullet, the tapering being referred to as the ogive. The bullet is typically housed within a cartridge, which also contains the propellant charge. At the base of the cartridge is the primer, which contains the primary explosive. When the primer is ignited, the resultant explosion detonates the propellant charge.
The bullet is positioned within a gun barrel, the purpose of which is to allow the bullet to quickly reach an acceptably high initial velocity using energy released when the propellant charge is detonated, and additionally to aim the bullet toward the target. The bullet is loaded into the barrel, with a driving band at the back end of the bullet being gripped by the rifling within the barrel. As the gun is fired, the primer is struck and thereby ignited by the firing pin, which in turn detonates the propellant charge. As the explosive powder burns, high gas pressure is built up in the chamber of the gun. When this gas pressure exceeds the pressure retaining the driving band in the rifling, the bullet is set in motion. At the exact moment the bullet leaves the barrel, the gas pressure exerted on the base of the bullet should be as uniform as possible to assure an accurate trajectory toward the intended target.
During the manufacturing process generally employed for conventional bullets, the bullet jackets, typically fabricated from copper tubing or nuggets, are filled with a weighted material, such as lead or a leaden component, by a variety of conventional methods. The lead within custom made bullets is often heat bonded to the copper jacket, while in the mass produced bullets, the lead typically is not heat bonded. Heat bonding is generally preferred as it enhances the weight retention of the bullet upon striking and penetrating the target, thereby increasing the penetration of the bullet.
When heat bonding methods are used, it can be difficult to properly form the base of the bullet. The base is generally formed by rolling the bottom edge of the bullet jacket inwardly to securely retain the lead within a cavity thereof. If too much pressure is applied to the base during the rolling process, the lead may be forced out of the bullet nose, thereby ruining the bullet. Thus, rolling the bottom edge of the jacket to form a base is a difficult process which has not always produced satisfactory results. As the amount of pressure which can be used in the rolling process is limited, the base of the conventionally produced bullet typically has a rounded edge which is not always uniform. In order to assure uniformity of the base, greater pressure is often needed, although it cannot always be effectively accommodated in heat bonded bullets. As discussed above, uniformity of the base is critical for accuracy, as the base is the last portion of the bullet to exit the firearm barrel. If gas is allowed to escape from one side of the barrel around one portion of the bullet base before it escapes from another side of the barrel, accuracy of the bullet trajectory will be compromised.
In order to achieve a more uniform base, it has been known in the past to reduce the pressure required to bend or roll the bottom portion of the jacket by reducing the width of this bottom portion using a milling tool to create an internal indentation therein. However, this milled indentation has not created a satisfactory product, as the rim portion having the reduced width is often weaker than a conventional rim, and the conventional bending process tends to create stress or even stress cracks around the outer lower circumference of the conventional bullet. In addition, the method by which the indentation is milled in the rim portion decreases the potential weight of the bullet, an undesired result in bullet manufacture.